Referring to FIG. 1, which is a schematic diagram for describing the prior art of Equirectangular Projection (ERP) method. Beginning from the top left, a fisheye camera 1 uses two fisheye lens 11, 12 back to back for catching images (step 1). Two fisheye pictures A and B are catched (step 2). The two fisheye pictures represent two hemispherical images respectively for having about 190°, so each has a loop 13, 14 about 5° at below respectively (step 3). The two hemispherical images are then spread into rectangular shapes to form two flat figures shown at the bottom left of FIG. 1 (step 4). This is so-called Equirectangular Projection (ERP) method of the prior art.
The two flat figures are each divided into two parts respectively, i.e. A-left, A-right and B-left, B-right. The left belt 131 of the A-left and the right belt 132 of the A-right are formed from the loop 13, each has about 10° (−95°˜−85° and 85°˜95°). The left belt 141 of the B-left and the right belt 142 of the B-right are formed from the loop 14, each has about 10° (−95°˜−85° and 85°˜95°).
The belt 132 and the belt 141 are stitched up, and the belt 131 and the belt 142 are stitched up, so as to form a panoramic image (step 5). At the end, the stitched panoramic image is projected to a 3-D ball sphere space to form a spherical panoramic picture (step 6).
The Equirectangular Projection (ERP) method is to transform spherical image into rectangular shape for forming two flat figures, so the arctic part and the antartic part have great distortion relative to the equator part.